Abstract: 4-Methylumbelliferone (4-MU) (M.W. 176), also known as hymechromone or 7-hydroxy-4-methylcoumarin, is a coumarin derivative with choleretic and spasmolytic properties. It is an approved drug for the treatment of biliary dyskinesia in Europe and Asia, where it is also consumed as a dietary supplement to improve liver health. 4-MU is known to inhibit biosynthesis of hyaluronic acid (HA), in part by competing with uridine diphosphate (UDP) as a substrate for UDP-glucuronosyltransferase (UGT). HA is synthesized by HA synthases from its precursors, UDP-glucuronic acid (UGA) and UDP-N-acetyl-glucosamine, both of which are generated by the UGT-mediated transfer of UDP to glucuronic acid and N-acetyl-glucosamine, respectively. By inhibiting UGT, 4-MU depletes the cytosolic pool of UGA, thereby reducing HA synthesis. 4-MU has also been shown to reduce the expression levels of HA synthases, although the impact of downregulations of these enzymes on HA synthesis is not fully understood. For over the last decade, 4-MU has been reported to exert anti-tumor and tumor-preventive activities in vitro and in vivo against wide spectrum of cancers, including cancers of prostate, kidney, pancreas, ovary, colon, liver and skin. These antitumor activities have been attributed to the ability of 4-MU to inhibit HA biosynthesis, as HA signaling is known to play a critical role in tumor initiation, growth, invasion, and neovascularization. Higher levels of HA and HAS have been demonstrated in more advanced and aggressive cancers. Using the transgenic adenocarcinoma of the prostate (TRAMP) mouse model, Dr. Vinata Lokeshwar and colleagues have previously reported that daily oral administration of 4-MU (450 mg/kg/day by gavage), started at 8 weeks, 12 weeks, or 22 weeks and continued through 28 weeks of age, significantly reduced prostate tumorigenesis without signs of overt toxicity in a treatment-timing dependent manner. TRAMP mice treated with 4-MU from 8 weeks or 12 weeks through 28 weeks of age had histologically normal prostates with areas of low-grade prostatic intraepithelial neoplasia (PIN), which is considered characteristic of the 8-week old TRAMP mice prostate, without any organ metastasis, while the vehicle control mice were found to have invasive adenocarcinoma of the prostate with metastatic lesions in the kidney, liver, and lung. The tumor suppressive effect of 4-MU continued to be observed in the TRAMP mice through 52 weeks of age even though the 4-MU treatment was stopped after 28 weeks. Moreover, the antitumor efficacy observed in the 4-MU treated mice was associated with the decreased levels of HA expression, accompanied by reduced Ki67-positive cells and microvessel density counts with the increased level of E-cadherin expression in the prostate tissue. These findings supported the potential utility of 4-MU as a nontoxic oral chemopreventive agent for prostate and other cancers. Pharmacokinetics and safety of 4-MU have previously been studied in clinical trials involving healthy volunteers and patients requiring cholecystectomy. Excellent safety profiles have been clinically demonstrated for short-term daily administrations of 4MU at 1200 mg to 2400 mg per day. Factors negatively affecting the utility of 4-MU are its short half-life (~30 min) and low oral bioavailability, which has been reported to be less than 3% in humans. 4-MU is extensively metabolized to a glucuronic acid (4-MUG) via UGT or a sulfate form (4-MUS). Glucuronidation is believed to account for more than 90% of 4-MU metabolism. 4-MUG is biliary eliminated and likely undergoes reabsorption from the intestine (enterohepatic recycling) for eventual elimination by the kidney, although pharmacokinetics (PK) of 4-MUG has not been well studied. Considering the working hypothesis for the mode of antitumor action of 4-MU, which requires a non-metabolized form of 4-MU molecule to serve as a competitive substrate for UGT, its tumor preventive activity may be significantly improved if a new formulation of 4-MU can be developed to target the lymphatic system while avoiding the first pass metabolism in the liver. Such a lymphatic targeting drug delivery approach is expected to increase 4-MU concentrations in non-hepatic organs. As a result of an application to the NCI PREVENT Cancer Preclinical Drug Development Program submitted by Dr. Vinata Lokeshwar of the Medical College of Georgia, Augusta University, a new formulation of 4-MU, 4-MU myristate (MUM), has been developed through the DCP Repository Program in coordination with PREVENT. The preliminary PK study of MUM conducted by the DCP Repository demonstrated that higher accumulations of 4-MU and its metabolite MUG were demonstrated in the bladder followed by the prostate in a multi-dosing mouse study. The data suggested that MUM may be useful for the prevention of invasive bladder cancer. The current study is focused on the further development of the newly formulated 4-MU, MUM, including the evaluation of its PK and pharmacodynamics (PD) profiles and tumor preventive efficacy using a preclinical model of bladder tumorigenesis.